Apparatus for scalable encoding/decoding of moving image and method thereof

ABSTRACT

Provided are a scalable encoding/decoding apparatus and method for the same for a moving image of more than 8 bits. The scalable moving image encoding apparatus includes a pixel value clipper clipping a pixel value of an original image to a pixel value with a predetermined pixel depth, a base layer encoder receiving the clipped image and encoding the clipped image using a predetermined encoding method based on motion prediction, a pixel value scaler receiving a base layer image generated by the base layer encoder, which is a decoded image of an encoded image, and scaling a pixel depth of the base layer image to the pixel depth of the original image, and an enhancement layer encoder subtracting the base layer image having a scaled pixel value from the original image to form an enhancement layer image and encoding the enhancement layer image using a predetermined encoding method.

BACKGROUND OF THE INVENTION

This application claims priority from Korean Patent Application No.10-2004-0037690, filed on May 27, 2004, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

1. FIELD OF THE INVENTION

The present invention relates to scalable encoding/decoding of a movingimage and, more particularly, to a scalable encoding/decoding apparatusand method for an 8-bit or larger moving image.

2. DESCRIPTION OF THE RELATED ART

Conventional moving image encoding/decoding technologies such as MPEG-2,MPEG-4, and JVT encode/decode a moving image of 8-bit pixels. Inparticular, MPEG-4 technology encodes/decodes a moving image of n bits,which is greater than eight bits, by, for example, expanding the dynamicscope of DCT coefficients or an Intra DC prediction table. However, whenencoding/decoding a moving image of 12-bit pixels, the conventionaltechnologies require a 12-bit based operation in a spatial domain and a16(12+4)-bit based operation in a frequency domain for motion estimationand compensation. Therefore, the conventional technologies needcomplicated encoders and decoders that are very different fromconventional 8-bit based moving image encoders and decoders. Inaddition, the conventional technologies do not support flexibleencoding/decoding based on bit length.

SUMMARY OF THE INVENTION

The present invention provides a flexible encoding/decoding apparatusand method of a moving image with more than an 8-bit pixel value, usinga conventional encoding/decoding technology of a moving image with an8-bit pixel value.

According to an aspect of the present invention, there is provided ascalable moving image encoder including a pixel value clipper clipping apixel value of an original image to a pixel value having a predeterminedpixel depth; a base layer encoder receiving a clipped image and encodingthe clipped image using a predetermined encoding method based on motionprediction; a pixel value scaler receiving a base layer image generatedby the base layer encoder, which is a decoded image of an encoded image,and scaling a pixel depth of the base layer image to the pixel depth ofthe original image; and an enhancement layer encoder subtracting thebase layer image having a scaled pixel value from the original image toproduce an enhancement layer image and encoding the enhancement layerimage using a predetermined encoding method.

The pixel value clipper may clip the pixel value of the original imageby a predetermined number of bits from a most significant bit until thepixel value of the original image becomes a pixel value having thepredetermined pixel depth.

The pixel value scaler may receive the base layer image and scale thepixel value of the base layer image to the pixel depth of the originalimage by listing the base layer image sequentially from a mostsignificant bit, moving bits of the base layer image to a same number ofhigh-order bits of the original image as the base layer image, andwriting zero to remaining bits of the original image. In addition, thebase layer encoder and the enhancement layer encoder may use an 8-bitbased moving image encoding method.

According to another aspect of the present invention, there is provideda scalable moving image decoder including a base layer decoder receivinga base layer bit stream created by clipping a pixel value of an originalimage to a predetermined pixel depth and encoding a clipped image usinga predetermined encoding method based on motion prediction, decoding thebase layer bit stream, and outputting a decoded base layer image; anenhancement layer decoder receiving an enhancement layer bit streamcreated by subtracting the decoded base layer image having a scaledpixel value from the original image and encoding the image obtained bysubtraction using a predetermined encoding method and decoding theenhancement layer bit stream; and a pixel value scaler receiving thedecoded base layer image and scaling a pixel value of the decoded baselayer image to the pixel depth of the original image.

The scalable moving image decoder may further include an adder adding adecoded enhancement layer image output from the enhancement layerdecoder to a scaled base layer image output from the pixel value scalerand outputting the result of addition.

According to another aspect of the present invention, there is provideda scalable moving image encoding method including clipping a pixel valueof an original image to a pixel value having a predetermined pixeldepth; receiving a clipped image and encoding the clipped image using apredetermined encoding method based on motion prediction; receiving adecoded image of an encoded image and scaling a pixel value of thedecoded image to the pixel depth of the original image; and subtractinga scaled image having a scaled pixel value from the original image andencoding a subtracted image using a predetermined encoding method.

According to another aspect of the present invention, there is provideda scalable moving image decoding method including receiving a base layerbit stream created by clipping a pixel value of an original image to apixel value having a predetermined pixel depth, encoding a clipped imageusing a predetermined encoding method based on motion prediction anddecoding the base layer bit stream, and outputting a decoded base layerimage; receiving an enhancement layer bit stream created by subtractingthe decoded base layer image having a scaled pixel value from theoriginal image and encoding the image obtained by subtraction using apredetermined encoding method and decoding the enhancement layer bitstream; and receiving the decoded base layer image and scaling a pixelvalue of the decoded base layer image to the pixel depth of the originalimage.

The scalable moving image decoding method may further include adding adecoded enhancement layer image output from the enhancement layerdecoder to a scaled base layer image output from the pixel value scalerand outputting the result of addition.

BRIEF DESCRIPTION OF THE DORIGINALINGS

The above and other aspects of the present invention will become moreapparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 illustrates video frames included in a moving image;

FIG. 2 is a block diagram of a conventional moving image encoder;

FIG. 3 is a block diagram of another conventional moving image decoder;

FIG. 4 is a block diagram of a scalable moving image encoder accordingto an exemplary embodiment of the present invention;

FIG. 5 illustrates a case where a pixel value clipper clips an n-bitpixel value to an 8-pixel value;

FIG. 6 illustrates a case where a pixel value scaler scales an 8-bitpixel value to an n-bit pixel value;

FIG. 7 is a block diagram of a scalable moving image decoder accordingto an exemplary embodiment of the present invention;

FIG. 8 is a flowchart illustrating a scalable moving image encodingmethod according to an exemplary embodiment of the present invention;and

FIG. 9 is a flowchart illustrating a scalable moving image decodingmethod according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. The invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth therein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the concept of the invention to those skilled in the art.

FIG. 1 illustrates moving image frames included in a moving image.Moving image data is encoded and decoded based on a motion predictiontechnology. A prediction is made with reference to a previous frame orboth previous and future frames based on a time axis. A frame referredto when encoding or decoding a current frame is called a referenceframe. In block-based moving image encoding, a still image (frame)included in a moving image is divided into a macro-block and amacro-block is divided into sub-blocks. Therefore, the motion of thestill image is predicted and encoded on a block-by-block basis.

Referring to FIG. 1, a moving image includes a series of still images.The still images are classified by group of pictures (GOP), and each ofthe still images is called a frame. One GOP includes an I frame 110, a Pframe 120, and a B frame 130. The I frame 110 is encoded without using areference frame. On the other hand, the P frame 120 and the B frame 130are encoded by motion estimation and compensation using the referenceframe.

FIG. 2 is a block diagram of a conventional moving image encoder. Themoving image encoder includes a motion estimator 210, a motioncompensator 220, a discrete cosine transform (DCT) performer 230, aquantizer 240, an entropy coder 250, a de-quantizer 260, an inverse DCT(IDCT) performer 270, a reference frame storage unit 280, and amultiplexer 290.

The motion estimator 210 searches the reference frame for a macro-blockand outputs the difference between the position of an image in themacro-block of the reference frame and the position of the image in amacro-block of a current frame as a motion vector. In other words, themotion estimator 210 searches for a desired macro-block within apredetermined search area of the reference frame, finds a macro blockmost similar to what was desired, and outputs the distance travelled bythe image, which is the difference between the position of the image inthe macro-block of the reference frame and that of the image in themacro-block of the current frame, as a motion vector. The motioncompensator 220 extracts a prediction macro-block corresponding to themotion vector from the reference frame and motion-compensates for theprediction macro-block of the reference frame.

Then, the motion-compensated prediction macro-block of the referenceframe is subtracted from the macro-block of the current frame. The DCTperformer 230 DCTs the result of the subtraction and outputs a DCTcoefficient. The quantizer 240 quantizes the DCT coefficient andtransmits the quantized DCT coefficient to the entropy coder 250. Theentropy coder 250 codes the quantized DCT coefficient and outputstexture information. The multiplexer 290 multiplexes the textureinformation together with the motion vector and outputs an encoded bitstream. When the current frame is the I frame, the DCT performer 230DCTs the macro-block of the current frame without motion estimation andcompensation and outputs a DCT coefficient. Then, the DCT coefficient isquantized, coded, and multiplexed by the quantizer 240, the entropycoder 250, and the multiplexer 290, respectively, and finally output asan encoded bit stream.

A value obtained by subtracting the motion-compensated macro-block ofthe reference image frame from the macro-block of the current frame iscalled a residual value. The residual value is encoded to reduce datavolume when encoding. Since errors occur in a quantizing process, amoving image created as a bit stream contains the errors that occurredin the DCT and the quantizing processes.

To obtain a reference frame, a quantized residual signal is passedthrough the de-quantizer 260 and the IDCT performer 270, combined with amotion-estimated/compensated image, and stored in the reference framestorage unit 280. When the current frame is the I frame, it is stored inthe reference frame storage unit 280 via the de-quantizer 260 and theIDCT performer 270 without motion-compensation. Therefore, a referenceframe stored in the reference frame storage unit 280 includes thecurrent frame with an encoded error that occurred in the DCT and thequantizing processes.

In other words, it is assumed that an original image (frame) is A and apredicted image (frame) after motion-estimation/compensation is B. TheDCT performer 230 receives A−B, which is a difference between theoriginal image and the predicted image, and DCTs the A−B. Since an errorcomponent E is created in the quantizing process, a bit stream outputfrom the IDCT performer 270 via the entropy coder 250 is (A−B)+E. Then,the predicted image B is added to (A−B)+E. Therefore, A+E, that is, theoriginal image plus the error component E, is stored in the referenceframe storage unit 280 as a reference frame.

FIG. 3 is a block diagram of a conventional moving image decoder.

The moving image decoder includes a motion compensator 310, an IDCTperformer 320, a de-quantizer 330, an entropy decoder 340, a referenceframe storage unit 350, and a de-multiplexer 360.

The encoded bit stream output from the moving image encoder of FIG. 2 isdivided into a motion vector and texture information by thede-multiplexer 360. The motion vector is transmitted to the motioncompensator 310, and the texture information is decoded by the entropycoder 340, the de-quantizer 330, and the IDCT performer 320. The motioncompensator 310 receives reference frame information from the referenceframe storage unit 350 and motion vector information from the movingimage encoder of FIG. 2 and outputs a predicted image. Then, thepredicted image is combined with a decoded image, and a combined imageis displayed.

FIG. 4 is a block diagram of a scalable moving image encoder accordingto an exemplary embodiment of the present invention.

The scalable moving image encoder includes a base layer encoder 410, anenhancement layer encoder 420, a pixel value clipper 430, and a pixelvalue scaler 440.

A moving image of any pixel depth may be input to the base layer encoder410 and the enhancement encoder 420, which may process a moving image ofany number of bits. Therefore, in this embodiment of the presentinvention, scalable encoding in which an n-bit moving image is processedas an 8-bit moving image will be described. An n-bit original movingimage is converted into an 8-bit moving image by the pixel value clipper430. The 8-bit moving image is encoded by the base layer encoder 410using a general 8-bit moving image encoding method.

A decoded image by the base layer encoder 410 is stored in a referenceimage storage such that the decoded image can be used formotion-estimation/compensation when the base layer encoder 410 performsencoding. To create an enhancement layer bit stream, the decoded imageis also transmitted to the pixel scaler 440 and scaled to the samenumber of bits (n bits) as the original image. A scaled image issubtracted from the original image, and the image resulting from thesubtraction is transmitted to the enhancement layer encoder 420. Theenhancement layer encoder 420 is a general 8-bit moving image encoderthat performs encoding based on motion-prediction. In the embodiment ofthe present invention, the base layer encoder 410 and the enhancementlayer encoder 420 may use MPEG-1, MPEG-2, MPEG-4, and H.264 encodingmethods.

FIG. 5 illustrates a case where the pixel value clipper 430 clips ann-bit pixel value to an 8-pixel value. To convert the n-bit pixel valueinto the 8-bit pixel value, eight high-order bits of the n-bit pixelvalue are clipped. In other words, eight high-order bits of the n-bitpixel value are cut to obtain the 8-bit pixel value composed of onlyeight most significant bits (MSB) of the pixel value of the originalimage.

FIG. 6 illustrates a case where the pixel value scaler 440 scales an8-bit pixel value to an n-bit pixel value.

To scale the 8-bit pixel value to the n-bit pixel value, eight bits ofthe 8-bit pixel value are moved to eight high-order bits of the n-bitpixel value, and zero is written to remaining bits of the n-bit pixelvalue. In this way, the 8-bit pixel value can be scaled to the n-bitpixel value.

FIG. 7 is a block diagram of a scalable moving image decoder accordingto an exemplary embodiment of the present invention.

The scalable moving image decoder includes a base layer decoder 710, anenhancement decoder 720, a pixel value scaler 730, and an adder 740.

In this exemplary embodiment of the present invention, the base layerencoder 710 and the enhancement layer decoder 720 may use MPEG-1,MPEG-2, MPEG-4, and H.264 decoding methods, which use 8-bit movingimages.

The base layer decoder 710, which receives an encoded bit stream(hereinafter, referred to as a base layer bit stream) output from thebase layer encoder 410 of FIG. 4, decodes the encoded base layer bitstream into an 8-bit moving image, stores the decoded 8-bit moving imagein a reference image storage, and outputs the decoded 8-bit moving imageto a pixel value scaler 730. The pixel scaler 730 scales the 8-bitmoving image to the n-bit moving image. The scaling process has beendescribed above with reference to FIG. 6.

The enhancement layer decoder 720 receives an encoded bit stream(hereinafter, referred to as an enhancement layer bit stream) outputfrom the enhancement layer encoder 420 of FIG. 4 and decodes theenhancement layer bit stream based on motion prediction. The adder 740combines an image output from the pixel value scaler 730 and an imageoutput from the enhancement layer decoder 720 into an n-bit image. Insome cases, only an image decoded by the base layer decoder 710 may bedecoded. In other words, when a network is not stable or when a lot oferrors occur, only the base layer bit stream can be decoded and outputeven though its image quality is not so good. Therefore, scalabledecoding is possible.

FIG. 8 is a flowchart illustrating a scalable moving image encodingmethod according to an exemplary embodiment of the present invention.Referring to FIG. 8, a pixel value of an original image is convertedinto a pixel value that can be processed by a decoder (Operation S810).Since an 8-bit decoder is used in the present invention, the pixel valueof the original image is clipped to the 8-bit pixel value. As describedwith reference to FIG. 5, 8 bits from the MSB are cut from the pixelvalue of the original image until the 8-bit pixel value is obtained.

The base layer encoder 410, which receives a clipped image, encodes theclipped image using a predetermined encoding method based on motionprediction, and outputs an encoded image as a base layer bit stream(Operation S820). Here, the encoding method may be a lossy encodingmethod. Then, the encoded image is decoded (Operation S830). A pixelvalue of the decoded image is scaled to the pixel value of the originalimage (Operation S840). The pixel value scaler 440 receives the decodedimage and scales the pixel value (8-bit pixel value) of the decodedimage to the pixel value (n-bit pixel value) of the original image bylisting the decoded image sequentially from the MSB, moving 8 bits ofthe 8-bit value to eight high-order bits of the n-bit pixel value, andwriting zero to the remaining bits of the n-bit pixel value of theoriginal image. Then, a scaled image is subtracted from the originalimage. The enhancement layer encoder 420 encodes a subtracted imageusing a predetermined encoding method and outputs an enhancement layerbit stream (Operation S850).

FIG. 9 is a flowchart illustrating a scalable decoding method of amoving image according to an exemplary embodiment of the presentinvention. Referring to FIG. 9, the base layer decoder 710 receives abase layer bit stream created by clipping a pixel value of an originalimage to a pixel value having a predetermined pixel depth and encodingthe clipped image using a predetermined encoding method based on motionprediction by the base layer encoder 410. The base layer decoder 710decodes the base layer bit stream and outputs a decoded base layer image(Operation S910). The enhancement layer decoder 720, which receives anenhancement layer bit stream from the enhancement layer encoder 420,decodes the enhancement layer bit stream and outputs a decodedenhancement layer image (Operation S920).

The pixel value scaler 730 receives the decoded base layer image andscales a pixel value of the decoded base layer image to the pixel valueof the original image (Operation S930). The scaling process has beendescribed above. The adder 740 adds the decoded enhancement layer imageto the decoded base layer image having a scaled pixel value and outputsthe result of the addition (Operation S940).

When a network is not stable or when a lot of errors occur, only thebase layer bit stream may be decoded and output even though its imagequality is not so good. The scalable moving image encoding and decodingmethod described above may be written as a computer program. Codes andcode segments of the computer program may be easily derived by computerprogrammers of ordinary skill in the art. The computer program isrecorded onto a computer-readable recording medium. The scalable movingimage encoding and decoding method is implemented when the computerprogram is read and executed by a computer. The computer readablerecording medium includes a magnetic recording medium, an opticalrecording medium, and a carrier wave medium.

As described above, a moving image encoding/decoding apparatus andmethod according to the present invention may store and transmit ann-bit moving image after encoding the n-bit moving image, using an 8-bitmoving image encoding/decoding technology, and decode and reproduce then-bit moving image.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A scalable moving image encoder comprising: a pixel value clipperwhich clips a pixel value of an original image to a pixel value having apredetermined pixel depth; a base layer encoder which receives a clippedimage and encodes the clipped image using a first predetermined encodingmethod based on motion prediction; a pixel value scaler which receives abase layer image generated by the base layer encoder, which is a decodedimage of an encoded image, and scaling a pixel depth of the base layerimage to a pixel depth of the original image; and an enhancement layerencoder which subtracts the base layer image having a scaled pixel valuefrom the original image to produce an enhancement layer image andencodes the enhancement layer image using a second predeterminedencoding method, wherein the enhancement layer encoder comprises amotion estimator and a motion compensator, and the second predeterminedencoding method used to encode the enhancement layer image is based onanother motion prediction.
 2. The scalable moving image encoder of claim1, wherein the pixel value clipper clips the pixel value of the originalimage by a predetermined number of bits from a most significant bituntil the pixel depth of the original image becomes equal to thepredetermined pixel depth.
 3. The scalable moving image encoder of claim1, wherein the pixel value scaler receives the base layer image andscales the pixel value of the base layer image to the pixel value of theoriginal image by listing bits of the pixel value of the base layerimage sequentially from a most significant bit, moving the bits of thepixel value of the base layer image to high-order bit positions of ascaled pixel value having a same number of bits as the pixel value ofthe original image, and writing zeros to remaining bit positions of thescaled pixel value.
 4. The scalable moving image encoder of claim 1,wherein the base layer encoder and the enhancement layer encoder use an8-bit based moving image encoding method.
 5. A scalable moving imagedecoder comprising: a base layer decoder which receives a base layer bitstream created by clipping a pixel value of an original image to apredetermined pixel depth and encoding a clipped image using a firstpredetermined encoding method based on motion prediction, decodes thebase layer bit stream, and outputs a decoded base layer image; anenhancement layer decoder which receives an enhancement layer bit streamcreated by subtracting a reference base layer image having a scaledpixel value from the original image and encoding an image obtained bythe subtracting using a second predetermined encoding method, decodesthe enhancement layer bit stream, and outputs a decoded enhancementlayer image; and a pixel value scaler which receives the decoded baselayer image and scales a pixel value of the decoded base layer image toa pixel depth of the original image, wherein the enhancement layerdecoder comprises a motion compensator, and decodes the enhancementlayer image bit stream based on another motion prediction.
 6. Thescalable moving image decoder of claim 5, further comprising an adderwhich adds the decoded enhancement layer image output from theenhancement layer decoder to a scaled base layer image output from thepixel value scaler and outputs a result of addition.
 7. The scalablemoving image decoder of claim 5, wherein the pixel value scaler receivesthe decoded base layer image from the base layer decoder and scales thepixel value of the decoded base layer image to the pixel depth of theoriginal image by listing bits of the pixel value of the decoded baselayer image sequentially from a most significant bit, moving the bits ofthe pixel value of the decoded base layer image to high-order bitpositions of a scaled pixel value having the same number of bits as thepixel value of the original image, and writing zeros to remaining bitpositions of the scaled pixel value.
 8. The scalable moving imagedecoder of claim 5, wherein the base layer decoder and the enhancementlayer decoder are 8-bit decoders.
 9. A scalable moving image encodingmethod comprising: clipping a pixel value of an original image to apixel value having a predetermined pixel depth; receiving a clippedimage and encoding the clipped image using a first predeterminedencoding method based on motion prediction; receiving a decoded image ofan encoded image and scaling a pixel value of the decoded image to thepixel depth of the original image; and subtracting a scaled image havinga scaled pixel value from the original image and encoding a subtractedimage using a second predetermined encoding method, wherein the secondpredetermined encoding method used to encode the subtracted image isbased on another motion prediction.
 10. The method of claim 9, whereinthe clipping of the pixel value of the original image comprises clippingthe pixel value of the original image by a predetermined number of bitsfrom a most significant bit to the predetermined pixel depth.
 11. Themethod of claim 9, wherein the receiving of the decoded image and thescaling of the pixel value of the decoded image comprises receiving thedecoded image and scaling the pixel value of the decoded image to thepixel depth of the original image by listing bits of the pixel value ofthe decoded image sequentially from a most significant bit, moving thebits of the pixel value of the decoded image to high-order bit positionsof a scaled pixel value having the same number of bits as the pixelvalue of the original image, and writing zeros to remaining bitpositions of the scaled pixel value.
 12. The method of claim 9, whereinthe predetermined number of bits is eight, and an 8-bit based encodingmethod is used for the receiving and encoding of the clipped image andthe subtracting of the scaled image and the encoding of the subtractedimage.
 13. A scalable moving image decoding method comprising: receivinga base layer bit stream created by clipping a pixel value of an originalimage to a pixel value having a predetermined pixel depth and encoding aclipped image using a first predetermined encoding method based onmotion prediction, decoding the base layer bit stream, and outputting adecoded base layer image; receiving an enhancement layer bit streamcreated by subtracting a reference base layer image having a scaledpixel value from the original image and encoding an image obtained bythe subtracting using a second predetermined encoding method, decodingthe enhancement layer bit stream, and outputting a decoded enhancementlayer image; and receiving the decoded base layer image and scaling apixel value of the decoded base layer image to a pixel depth of theoriginal image, wherein the second predetermined encoding method isbased on another motion prediction.
 14. The method of claim 13, furthercomprising adding a decoded enhancement layer image output from anenhancement layer decoder to a scaled base layer image output from thepixel value scaler and outputting a result of addition.
 15. The methodof claim 13, wherein the receiving of the decoded base layer image andthe scaling of the pixel value of the decoded base layer image comprisesreceiving the decoded base layer image from the base layer decoder andscaling the pixel value of the decoded base layer image to the pixeldepth of the original image by listing bits of the pixel value of thedecoded base layer image sequentially from a most significant bit,moving the bits of the pixel value of the decoded base layer image tohigh-order bit positions of a scaled pixel value having the same numberof bits as the pixel value of the original image, and writing zeros toremaining bit positions of the scaled pixel value.
 16. A non-transitorycomputer-readable recording medium recording a program executing ascalable moving image encoding method in a computer, the scalable movingimage encoding method comprising: clipping a pixel value of an originalimage to a pixel value having a predetermined pixel depth; receiving aclipped image and encoding the clipped image using a first predeterminedencoding method based on motion prediction; receiving a decoded image ofan encoded image and scaling a pixel value of the decoded image to thepixel depth of the original image; and subtracting a scaled image havinga scaled pixel value from the original image and encoding the imageobtained by subtraction using a second predetermined encoding method,wherein the second predetermined encoding method used to encode thesubtracted image is based on another motion prediction.
 17. Anon-transitory computer-readable recording medium recording a programexecuting a scalable moving image decoding method in a computer, thescalable moving image decoding method comprising: receiving a base layerbit stream created by clipping a pixel value of an original image to apixel value having a predetermined pixel depth and encoding a clippedimage using a first predetermined encoding method based on motionprediction, decoding the base layer bit stream, and outputting a decodedbase layer image; receiving an enhancement layer bit stream created bysubtracting a reference base layer image having a scaled pixel valuefrom the original image and encoding the image obtained by thesubtracting using a second predetermined encoding method, decoding theenhancement layer bit stream, and outputting a decoded enhancement layerimage; and receiving the decoded base layer image and scaling a pixelvalue of the decoded base layer image to a pixel depth of the originalimage, wherein the second predetermined encoding method is based onanother motion prediction.